1. Field of the Invention
The present invention relates to fin assemblies and more particularly to quick change fin assemblies for attachment to a buoyant test vehicle (BTV), the assemblies having fin bodies bolted to a T-shaped base, the T-shaped base fitting into a T-shaped slot cut into the BTV. The fin assemblies are held in place by a BTV end piece which is attached to the BTV after the fin assemblies have been fit into the slot. When in place, the end piece closes off the T-shaped slot, preventing the release of the fin assemblies. A resilient sheet is placed between the fin body and the base to absorb noise and stress.
2. Description of the Prior Art
BTV's are used to test noise generated by shapes moving through a fluid medium. The BTV is configured to conform to the desired shape, hauled down below the water surface and released. Noise measurements are taken as the BTV rises to the surface. Depending on the release depth, the BTV can reach significant speed in rising to the surface such that it may rise to altitudes of one hundred and twenty feet after broaching the surface. Typically, the BTV then drops tail first back into the water, often breaking one or more fins when striking the water surface. The fins of prior art BTV's are bolted to the tail section of the BTV either with very long bolts extending through the fin and engaging the tail section, or with shorter bolts counter sunk in very deep bores within the fin. In prior art fin assemblies using long bolts, the long bolts bend when the BTV strikes the water surface making the removal of the fin assembly for replacement difficult. Prior art fin assemblies using shorter bolts are difficult to manufacture because of the deep bores required. In both the long bolt and short bolt prior art assemblies, the bores are filled above the bolts such that the bores do not contribute to any turbulence along the fins which would adversely impact noise measurements. Wax is typically used to fill the bores, the wax being easily pored into the bores once the bolts have been inserted. The wax is also easily removed to obtain access to the bolts in order to replace the fins. However, the use of wax requires the BTV to be removed from the water when a fin is replaced.
Removable or changeable fin assemblies are well known in the art. Such assemblies, as illustrated by Morey et al. (U.S. Pat. No. 3,516,099), typically consist of a fin and base bolted or wedged into a mounting box provided in the structure to which the fin assembly is attached. In other prior art assemblies, as illustrated by Kline (U.S. Pat. No. 2,119,881) and Fry (U.S. Pat. No. 5,007,868), a tongue and groove joint provides for the attachment of the fin assembly to the structure. Kline discloses a T-shaped keel or fin tightly engaging a corresponding rib on a rowboat. Fry discloses a tapered, dovetail-shaped groove on a fin or skeg for slidingly attaching the fin or skeg to a corresponding dovetail tongue on a marine propulsion device. With the exception of the prior art fin assemblies currently used on BTV's, the prior art removable fin assemblies do not provide the non-turbulent fin mountings necessary for conducting sensitive noise measurements. Additionally, the prior art methods for connecting the fin assemblies to the respective structures transmit vibrations from the fins to the structure. During a BTV test, such vibrations would interfere with acoustic measurements being taken.